Electric sails are a promising propulsion method for relatively low-cost and high-performance spacecraft within the solar system. They are similar to solar sails, but use solar wind as a source of thrust.
In known designs the electric sail consists of tethers arranged radially from a central, rotating hub, or of some kind of network of wires, tethers, or similar narrow structures covering a relatively large area. Solar sail designs frequently use thin foil.
For further information on the state of the art in electric sails, see the US patent application 2007/0205331 A1 (P. Janhunen: Electric Sail for Producing Spacecraft Propulsion); P. Janhunen: Electric Sail for Spacecraft Propulsion, AIAA Journal of Propulsion and Power, 20(4), 2004; P. Janhunen & A. Sandroos: Simulation study of solar wind push on a charged wire: basis of solar wind electric sail propulsion, Annales Geophysicae, 25, pp. 755-767, 2007; and P. Janhunen: On the feasibility of a negative polarity electric sail, Annales Geophysicae, 27, pp. 1439-1447, 2009; and the presentation by P. Janhunen on the state of the art in electric sails presented at the First Workshop on Electric Sailing held at ESA ESTEC on Monday, May 19, 2008. The above references are hereby incorporated herein by reference.
The efficiency of an electric sail is proportional to the effective area of the sail, which in turn depends on the voltage in the tethers. However, increasing the voltage of the tethers is difficult, because near the hub the tethers are relatively close to each other, and controlling very high voltages and voltage differentials becomes difficult, especially in confined spaces within a spacecraft.
It is an objective of the present invention to make use of much higher tether voltages possible, therefore increasing the effective area of the sail without necessarily increasing its physical dimensions.